The present invention relates to shaft for use in machines. In particular, the present invention relates to flexible shafts comprised of at least two rigid, tubular, shell-like portions containing, and linked together by a flexible, moldable material.
While the present invention has utility in apparatus comprising various mechanical components, it has particular application, and will therefore be described with reference to, electrostatographic printers. FIG. 1 illustrates an exemplary electrostatographic printer 8. That printer includes a photoconductive drum 10 that rotates in the direction 11. The surface of the drum 10 is charged to a substantially uniform potential by a corotron 12. The charged drum is then exposed to a light image of an original document 15 on an exposure platen 16 by means of an exposure lamp 17. The original document is moved over the exposure platen such that the full document is exposed to light from the exposure lamp. The light image of the original document discharges the charged surface of the drum so as to create an electrostatic latent image of the original document. A developer 20 then deposits toner on the electrostatic latent image so as to produce a toner image of the images on the original document 15. The toner image is comprised of charged toner particles that triboelectrically adhere to the electrostatic latent image. The toner image is subsequently transferred at a transfer station 24 onto a substrate 21, which is fed by a paper tray feeder 22 into intimate transfer contact with the toner image. The transferred toner image is then permanently affixed to the substrate by heat and/or pressure in a fuser 23. After transfer, residual toner, paper particles, dust, or other debris on the drum 10 is removed by a cleaner 26 in preparation for the next imaging cycle.
While FIG. 1 provides a simplified description of an exemplary electrostatographic printer, in practice such printers are far more complex. For example, such printers include numerous electrical subsystems, such as digital controllers and power supplies, and mechanical subsystems that rotate the drum, move substrates through the machine, and sort and staple image-bearing substrates together. For example, FIG. 2 illustrates a simplified view of the paper tray feeder 22. That feeder includes a tray for holding substrates 30 and an upper frame member 26 that closes over the tray. The upper frame member selectively removes the top substrate from the paper tray and feeds it as described above. To assist removal and feeding, the upper frame member includes two shafts, the shafts 32 and 34. Those shafts retain gears, rolls, pulleys, and friction surfaces, may include retention or location features such as, snaps, fitting elements or stops, and may contain other features such as bearings, bushings, rollers, journals and 0-rings. When a gear 36 on the shaft 32 is rotated by an external drive, a friction surface 38 contacts the topmost substrate and advances it toward the shaft 34. The shaft 34 is rotated by a drive belt 35 connected on a pulley 37 and a pulley 39. The shaft 34 includes rollers that further advance the substrate into the remainder of the printer.
In the prior art most electrostatographic printing machines used shafts made from solid materials such as steel and aluminum. Functional features or elements, such as rollers or gears, were then individually mounted on the shaft or were formed in place using metal working techniques such as turning, milling and grinding. Therefore, the completed shaft required significant manual labor. While satisfactory in many respects, the resulting shaft assemblies were rigid, heavy, and costly.
While rigid shafts are beneficial in many applications, in other applications some flexibility is beneficial. For example, when a rigid shaft is used to couple a driven element to a drive element careful alignment is required. Even a relatively minor misalignment can introduce destructive bending, vibration, and torque. However, flexible shafts can reduce alignment problems. In addition to reducing alignment problems highly flexible shafts can transmit forces around bends and corners.
Attempts have been made to provide shaft assemblies with reduced weight and cost. One approach is to use a composite shaft process. The composite shaft process may be more fully understood with reference to U.S. Pat. No. 5,439,916; U.S. Pat. No. 5,876,288; and U.S. Pat. 5,683,641. The composite shaft process utilizes a hollow metal tube into which slits or holes are machined through the wall of the tube. The tube is then placed in a molding machine and a moldable material is injected into the opening on the end of the tube and passed through the slits or holes to fill functional features formed in a mold cavity. While the composite shaft process provides for improved performance and reduce costs, the use of a cylindrical metal tube adds costs to the shaft assembly.
U.S. patent application Ser. No. 09/293,346, entitled xe2x80x9cHollow Shafts with Gas Assist Molding,xe2x80x9d filed on Apr. 16, 1999 and U.S. patent application Ser. No. 09/293,098, entitled xe2x80x9cPlastic Shafts with Molded Core and External Feature,xe2x80x9d filed on Apr. 16, 1999 teach a molding process for plastic tubes. According to those patents a hollow plastic tube having slits or holes is placed in a molding machine. A moldable material is injected into the slits or holes via the end of the tube. The moldable material passes through the slits or holes to fill functional features in a mold cavity.
While the teachings of U.S. patent application Ser. No. 09/293,346 and U.S. patent application Ser. No. 09/293,098 are beneficial, they produce rigid shafts. Therefore, it would be even more beneficial to extend those teachings to enable production of flexible shaft assemblies.
The principles of the present invention provide for molded, flexible shaft assemblies. A molded, flexible shaft assembly according to the principles of the present invention is comprised of at least two rigid, tubular, shell-like portions containing, and linked together by, a flexible, moldable material. Beneficially the moldable material is polyurethane.